LTT CREW CANCELED IFR AND FLEW VFR IN IMC CONDITIONS. THEY CUT OUT A BARON TO LAND DOWNWIND AT TRM.

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ON IFR FLT PLAN FROM PHX TO UDD. WX WENT BELOW IFR MINIMUMS AT PSP AND UNABLE TO GO VFR INTO UDD. ELECTED TO SHOOT VOR APCH INTO TRM AND PROCEED VFR TO UDD IF ABLE; OR LAND AT TRM. MDA FOR VOR APCH IS APPROX 380 FT MSL. BROKE OUT OF CLOUDS AT ABOUT 700 FT; ELECTED TO LAND TRM DUE TO LOW CEILING AND POOR VISIBILITY; 2 MI AT BEST IN STEADY RAIN. AFTER GETTING TRM IN SIGHT; FO CANCELED IFR WITH PSP APCH CTL; THEN MADE ANNOUNCEMENT OF LNDG ON RWY 35 AT TRM. THE PROB WAS WE WERE ON THE WRONG FREQ. USED UDD FREQ OF 122.8 INSTEAD OF TRM FREQ. I SAW NO TARGETS ON OUR TCASII AND LANDED ON RWY 35. ON LNDG ROLLOUT; A TWIN BARON INBOUND TO LAND ON RWY 17 WENT AROUND; WIND FAVORED RWY 17; BUT IN LIGHT OF RWY LENGTH CEILING AND VISIBILITY CONDITIONS; I ELECTED TO LAND STRAIGHT IN ON RWY 35. THERE WERE NO OTHER IFR TFC AT THE TIME; BECAUSE ONLY 1 ACFT CAN SHOOT ON APCH AT A TIME; MY ACFT WAS IN ERROR BEING ON THE WRONG CTAF FREQ TO MAKE ANNOUNCEMENTS BUT FEEL THE TWIN BARON SHOULD NOT HAVE BEEN FLYING AROUND VFR WITH IFR CONDITIONS. I ALSO SUSPECT THE TWIN BARON HAD THEIR XPONDER OFF; NOT ALLOWING ME TO GET A TCASII ALERT.